7 September 2017 Investigation of HF-plasma-treated soft x-ray optical elements
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The contamination of optical elements (mirrors and gratings) with carbon still is an issue when using soft x-ray synchrotron radiation. With an in-house developed HF-plasma treatment we are able to decontaminate our optics in-situ from carbon very efficiently. The cleaning device, a simple Al-antenna, is mounted in situ inside the mirror- and grating vacuum chambers. A systematic study of the HF-plasma cleaning efficiency was performed acquired with in-situ and exsitu methods for monitoring: An atomic force microscope (AFM) and a scanning tunneling microscope (STM) were used before and after the cleaning process to determine the surface morphology and roughness. Reflectivity angular scans using the reflectometer at the BESSY-II Metrology Station [1-3] allowed to estimate the thickness of the remaining Clayer after different cleaning steps and thereby helped us to determine the etching rate. Reflection spectra measurements in the range of 200 eV – 900 eV show the complete removal of Carbon from the optics without contaminating it with any other elements due to the plasma treatment. The data show that the plasma process improves the reflectivity and reduces the roughness of the surface. In addition to that, the region of the optical surface where the carbon has been removed becomes passivated.
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F. Eggenstein, F. Eggenstein, M. Krivenkov, M. Krivenkov, I. Rudolph, I. Rudolph, M. G. Sertsu, M. G. Sertsu, A. Sokolov, A. Sokolov, A. Varykhalov, A. Varykhalov, J. Wolf, J. Wolf, T. Zeschke, T. Zeschke, F. Schäfers, F. Schäfers, } "Investigation of HF-plasma-treated soft x-ray optical elements", Proc. SPIE 10385, Advances in Metrology for X-Ray and EUV Optics VII, 1038505 (7 September 2017); doi: 10.1117/12.2272967; https://doi.org/10.1117/12.2272967

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